A cooling fan is a very commonly used means for cooling and dissipating heat and is mainly installed in an electronic or electrically powered unit to discharge heat generated by the electronic or electrical unit during its operation. By this way, the electronic and/or electrical unit and the elements thereof are adequately protected from being damaged by the high temperature and thereby have prolonged life. Most of the office machines, such as the main unit of computers, video tape recorders and copiers, are equipped with a cooling fan.
A conventional cooling fan 60, as shown in FIG. 5, usually includes a blade support 61 and main body 62. The blade support and 61 has a hollow central support from a circumferential periphery thereof a plurality of blades 611 are provided. A magnet 612 is fittingly attached to an inner wall of the hollow central support and a central locating shaft 613 axially projects forward from the hollow central support. The main body 62 has a fixedly centered blade holder 621 which includes a backward extended column 622. The column 622 has an axially extended central through hole 623. A middle portion of the through hole 623 is radially raised to form a circle of bearing surface 624 to receive a self-lubricating bearing 63 therein. The self-lubricating bearing 63 has a central shaft hole 631 formed therein to receive the locating shaft 613 of the blade support 61. A circuit board 625 and a coil 626 are provided outside the column 622 for electrically controlling the movement of blades 611.
To assemble the cooling fan 60, directly insert the locating shaft 613 of the blade support 61 into the shaft hole 631 of the bearing 63; a first and a second oil ring 614, 615 having a round cross section are put over the locating shaft 613 to contact a rear and a front end surface of the self-lubricating bearing 63, respectively. A retaining ring 616 positioned in front of the second oil ring 615 is used to hold the locating shaft 613 so that a front head portion of the latter is securely kept projecting out of the shaft hole 631. The magnet 612 is provided at an outer periphery of the coil 626 such that the locating shaft 613 rotates in the shaft hole 631 relative to the self-lubricating bearing 63 to turn the blade support 61 and the blades 611, accordingly, when the circuit board 625 and the coil 626 are electrically made.
When the locating shaft 613 rotates relative to the self-lubricating bearing 63, lubricant pre-stored in the latter will be released from sintering pores of the bearing 63 to lubricate the same and the locating shaft 613.
The above lubricating system usually adopted by the conventional cooling fans has the following shortcomings. Please refer to FIG. 6, when the first and the second oil rings 614, 615 rotate with the locating shaft 613, a friction generated between the oil rings 614, 615 and the end surfaces of the self-lubricating bearing 63 shall suck a part of the lubricant in the self-lubricating bearing 63 from the sintering pore of the latter. The sucked lubricant shall then be jetted around due to the centrifugal force generated during the rotation of the oil rings 614, 615. A part of the lubricant jetted from the first oil ring 614 flows out of the through hole 623 of the column 622 via gaps 71 between the end surface of the bearing 63 and the oil ring 614 and therefore, causes the lubricant inside the bearing 63 to gradually lose and decrease. When the lubricant inside the self-lubricating bearing 63 is exhausted, no lubricant ban be used to lubricate the locating shaft 613 and the bearing 63 and over friction will be caused during further rotation of the locating shaft 613 in the bearing 63. The locating shaft 613 and the bearing 63 are both easily worn and damaged to produce noise and shorten the usable life of cooling fans 60 under this no-lubrication condition.
Lubricant jetted from the second oil ring 615 is retained in a closed room of the through hole 623 between a front end surface of the bearing 63 and an oil cap covered in front of the blade holder 621 and has not any lubricating effect on the bearing 63 itself and on the end surface of the bearing 63 contacting the first oil ring 614, but to locally lubricate the end surface of the bearing 63 contacting the second oil ring 615 via natural flowing.
Since the bearing and the oil rings are important parts in the lubricating system of a cooling fan, it is necessary to have a new lubricating system with desirable structure to use with a cooling fan, so that the oil loss rate of the self-lubricating bearing can be minimized to prolong the life of the cooling fan and to better smooth the rotating of the locating shaft of the blades.